Though the Chinese fishing fleets had successfully harvested flying squid in the North Pacific in recent years, they met the great problem in 2001. In order to illustrate the reason of severer reduction in harvest, the environment structure, the dorsal mant le length compositions of flying squid and the stomach contents of some harvested squid have been analyzed. The wandering of Kuroshio in south of Japan, the puniness of Kuroshio, and the cooler of the water in the northern part of the ocean are the known disadvantages in hydrologic structure. The reduction in abundance of f lying squid in the western part of the ocean was the important reason for declining of the catch in the area. The poor food abundance happened to be another unfavorable factor. But in the eastern part of the ocean, what worked most on the failure of production was the poor acknowledge of the schools, which caused an earlier withdrawal of f ishing vessels from the waters when there were some difficult ies in searching of the schools.